Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-coated tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
When such CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached should be detected. With respect to the thickness of an oxide film, polishing speed etc., the polishing treatment of a test wafer has been conducted by periodically treating the wafer, and after the results are confirmed, a wafer serving as a product is subjected to polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and a test wafer and a product wafer not subjected to processing are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there is need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. For such detection, various methods have been used, and from the viewpoint of measurement accuracy and spatial resolution in non-contact measurement, an optical detection means is becoming the mainstream.
The optical detection means is specifically a method of detecting the end-point of polishing by irradiating a wafer via a polishing pad through a window (light-transmitting region) with a light beam, and monitoring an interference signal generated by reflection of the light beam.
As the light beam, a white light using a halogen lamp having a light of wavelengths of 300 to 800 nm is generally used at present.
In such method, the end-point is determined by knowing an approximate depth of surface unevenness through monitoring of a change in the thickness of a surface layer of a wafer. When such change in thickness becomes equal to the thickness of the unevenness, the CMP process is finished. As a method of detecting the end-point of polishing by such optical means and a polishing pad used in the method, various methods and polishing pads have been proposed.
For example, a polishing pad having, as least a part thereof, a solid and uniform transparent polymer sheet passing a light of wavelengths of 190 nm to 3500 nm therethrough is disclosed (Patent Literature 1). Further, a polishing pad having a stepped transparent plug inserted therein is disclosed (Patent Literature 2). A polishing pad having a transparent plug on the same surface as a polishing surface is disclosed (Patent Literature 3).
As described above, a white light using a halogen lamp or the like is used as the light beam, and when the white light is used, there is an advantage that the light of various wavelengths can be applied onto a wafer, and many profiles of the surface of the wafer can be obtained. When this white light is used as the light beam, detection accuracy should be increased in a broad wavelength range. However, a polishing pad having a conventional window (light-transmitting region) has a problem that the polishing pad is very poor in detection accuracy at the short-wavelength side (ultraviolet region) and causes mechanical errors in detection of the optical end-point. In high integration and micronization in production of semiconductors in the future, the wiring width of an integrated circuit is expected to be further decreased, for which highly accurate optical end-point detection is necessary, but the conventional window for end-point detection does not have sufficiently satisfactory accuracy in a broad wavelength range (particularly at the short-wavelength side).
Meanwhile, there are proposals for preventing a slurry from leaking from the boundary (joint) between a polishing region and a light-transmitting region (Patent Literatures 4 and 5). For preventing slurry leakage, a method of arranging a transparent film coated on the upper side and underside thereof with an adhesive between an upper-layer pad and a lower-layer pad is disclosed (Patent Literature 6). However, the above-mentioned problem of low detection accuracy at the short-wavelength side has never been solved.
Patent Literature 1: JP-A 11-512977
Patent Literature 2: JP-A 9-7985
Patent Literature 3: JP-A 10-83977
Patent Literature 4: JP-A 2001-291686
Patent Literature 5: JP-A 2003-510826
Patent Literature 6: JP-A 2003-68686